Thin-film Composite Reverse Osmosis Membranes Research Articles

Modification of PSf/SPSf Blended Porous Support for Improving the Reverse Osmosis Performance of Aromatic Polyamide Thin Film Composite Membranes.

In this study, modification of polysulfone (PSf)/sulfonated polysulfone (SPSf) blended porous ultrafiltration (UF) support membranes was proposed to improve the reverse osmosis (RO) performance of aromatic polyamide thin film composite (TFC) membranes. The synergistic effects of solvent, polymer concentration, and SPSf doping content in the casting solution were investigated systematically on the properties of both porous supports and RO membranes. SEM and AFM were combined to characterize the physical properties of the membranes, including surface pore natures (porosity, mean pore radius), surface morphology, and section structure. A contact angle meter was used to analyze the membrane surface hydrophilicity. Permeate experiments were carried out to evaluate the separation performances of the membranes. The results showed that the PSf/SPSf blended porous support modified with 6 wt % SPSf in the presence of DMF and 14 wt % PSf had higher porosity, bigger pore diameter, and a rougher and more hydrophilic surface, which was more beneficial for fabrication of a polyamide TFC membrane with favorable reverse osmosis performance. This modified PSf/SPSf support endowed the RO membrane with a more hydrophilic surface, higher water flux (about 1.2 times), as well as a slight increase in salt rejection than the nascent PSf support. In a word, this work provides a new facile method to improve the separation performance of polyamide TFC RO membranes via the modification of conventional PSf porous support with SPSf.

Performance of Reverse Osmosis Membranes in the Treatment of Flue-Gas Desulfurization (FGD) Wastewaters

Reverse osmosis (RO) was studied to reduce salinity of flue gas desulfurization (FGD) wastewaters after softening with Na2CO3·H2O and ultrafiltration (UF). Two commercial thin film composite polyamide RO membranes (SWC-2540 and ESPA-2540, from Hydranautics) in spiral-wound configuration were tested and their performance in terms of salinity reduction as well as permeate flux, fouling index and water recovery was evaluated. Experimental runs were performed according to the feed and bleed configuration in selected operating conditions. For the SWC-2540 membrane experiments were also performed in total recycle configuration in order to evaluate the effect of operating pressure on permeate flux and quality. Experimental results indicated that the SWC-2540 membrane showed a better performance in the rejection of ions: Mg2+ ions were completely rejected, while the rejection towards monovalent ions such as Na+ was of about 95.5%. The ESPA-2540 membrane showed rejections towards Ca2+ and Mg2+ higher than 86.5% whilst the observed rejection towards Na+ was of 80%. For the SWC-2540 membrane an increased rejection for Ca2+ and Na+ ions was observed by increasing the operating pressure in the range 16-50 bar. Mg2+ ions were totally rejected independently by the operating pressure.

Incorporation of Quorum Sensing Inhibitors onto Reverse Osmosis Membranes for Biofouling Prevention in Seawater Desalination

Abstract Membrane biofouling, caused by bacterial biofilm formation is a significant obstacle for membrane filtration processes because it reduces pure water permeability. Recent studies have shown that bacterial communication pathways, known as quorum sensing (QS), trigger biofilm development. QS inhibiting compounds (QSIs) have been identified as an important key to disrupt QS pathways and ultimately reduce biofilm production. In this study, two known QSIs, vanillin and cinnamaldehyde, were physically attached onto polyamide thin-film composite reverse osmosis (RO) membranes to enhance membrane in situ antibiofouling potential. QSI attachment altered the membrane surface contact angle to reflect the property of the QSI, but there were no significant changes in salt rejection and pure water permeability. Under biofouling conditions, the QSI-modified RO membranes experienced a minimal loss in permeate flux compared with one of the control membranes in a high-pressure RO system. QSI attachment significantl...

Polyamide thin-film composite membrane modified with persulfate for improvement of perm-selectivity and chlorine-resistance

Polyamide (PA) thin-film composite (TFC) reverse osmosis membrane is widely used for desalination, but the selectivity-permeability trade-off and oxidation are two major restrictions on the membrane application. By modifying PA TFC membrane with potassium persulfate (K2S2O8), we overcame the trade-off relation (the water flux and salt rejection increased by 43.2% and 0.2%, respectively) and improved the chlorine resistance. The modification was demonstrated to be a combination of the interfacial crosslinking between PA layer and polysulfone support with the surficial oxidation of PA layer. The dense crosslinked interface enabled the membrane with higher solute rejection, better chlorine tolerance and long-term stability. Meanwhile, the thinner PA layer contributed to the increase of membrane permeability. Furthermore, the modification method has the application potential in high-performance membrane fabrication in terms of simplicity and high efficiency.

A novel pathway for high performance RO membrane: Preparing active layer with decreased thickness and enhanced compactness by incorporating tannic acid into the support

We report a novel pathway for preparing polyamide (PA) thin-film composite (TFC) reverse osmosis (RO) membrane with high permselectivity by incorporating tannic acid (TA) into the polysulfone (PSf) support. The support and RO membrane were characterized systematically. The results showed that (1) the support surface was enriched with TA due to the high hydrophilcity of TA and (2) TA endowed the RO membrane with a thinner and more compact PA active layer. The influencing mechanism of TA on the PA layer formation was discussed. TA affected the formation of PA layer through changing the m-phenylenediamine (MPD) molecules absorption behavior and the formation of the nascent film. The RO membrane desalination performances for both brackish water and seawater were evaluated. Due to the thinner and more compact PA active layer, PSf/TA-RO (the membrane prepared on PSf/TA support) possessed a higher rejection and a comparative flux compared to PSf-RO (the membrane prepared on PSf support). This work provides an effective way for preparing high performance RO membranes via utilizing support to tailor the aqueous phase monomer absorption and the formation of the nascent film.

Triclosan-immobilized polyamide thin film composite membranes with enhanced biofouling resistance

We report on a strategy to improve biofouling resistance of a polyamide (PA) thin-film composite (TFC) reverse osmosis (RO) membrane via chemically immobilizing triclosan (TC), known as a common organic biocide, on its surface. To facilitate covalent attachment of TC on the membrane surface, TC was functionalized with amine moiety to prepare aminopropyl TC. Then, the TC-immobilized TFC (TFC-TC) membranes were fabricated through a one-step amide formation reaction between amine groups of aminopropyl TC and acyl chloride groups present on the PA membrane surface, which was confirmed by high-resolution XPS. Strong stability of the immobilized TC was also confirmed by a hydraulic washing test. Although the TFC-TC membrane showed slightly reduced separation performance compared to the pristine control, it still maintained a satisfactory RO performance level. Importantly, the TFC-TC membrane exhibited excellent antibacterial activity against both gram negative (E. coli and P. aeruginosa) and gram positive (S. aureus) bacteria along with greatly enhanced resistance to biofilm formation. Our immobilization approach offers a robust and relatively benign strategy to control biofouling of functional surfaces, films and membranes.

High-performance reverse osmosis membranes fabricated on highly porous microstructured supports

Increasing the surface porosity of a support membrane has been proposed as an effective way to improve the water permeability of thin-film composite (TFC) reverse osmosis (RO) membranes by reducing the diffusion pathway in the active layer. In this work, we prepared a highly porous microstructured (HPμS) support membrane with a suitable mechanical strength to enhance the water permeability of an RO membrane. The HPμS support membrane was prepared by increasing the thermodynamic instability of a 10 wt% polymer solution and thereby facilitating rapid desolvation. The rapid desolvation formed the narrow and regularly arranged pore structure in the sublayer, and we proposed the mechanism for the sublayer structure formation based on analyses of the thermodynamic properties of such a binary system. Owing to the narrow and regular structure, the HPμS support membranes showed the exceptional mechanical strength, which was comparable to the strength of support membranes used for conventional RO membranes. Also, the HPμS support membranes successfully endowed an in-house RO membrane with the performance (water permeability of 4.68 L m−2 h−1 bar−1 and NaCl rejection of 98.3%) surpassing commercial RO membranes and thin-film nanocomposite membranes recently reported in the literature.

Antibiofouling thin-film composite membranes (TFC) by in situ formation of Cu-(m-phenylenediamine) oligomer complex

In situ formation of a Cu-(m-phenylenediamine) (Cu-mPD) oligomer complex from copper chloride during the interfacial polymerization process was successfully employed to produce modified thin-film composite reverse osmosis membranes (TFC-RO) with antibiofouling properties. Membranes were characterized by field emission scanning electron microscopy, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), atomic force microscopy, and contact angle measurements. Antibiofouling properties were studied using a colony-forming unit test with Escherichia coli. Moreover, an antiadhesion test was developed using fluorescence microscopy. Membrane performance using a cross-flow cell was evaluated, and copper concentration in permeate water was measured. FTIR, XPS and XRD results confirmed the formation of a Cu-mPD oligomer complex and its incorporation into the polyamide layer. A mechanism for formation of the oligomer within the membrane was proposed based on the interaction between the oxygen of the carbonyl group of the polyamide layer and copper ion of the Cu-mPD oligomer complex. The modified membrane showed a slight decrease in hydrophilicity and higher surface roughness. However, excellent antibacterial and antiadhesion effects were observed, attributed to copper toxicity as a result of Cu2+ ions release from the membrane surface. Release of copper ions in the permeate water was determined, and the maximum value observed was considered negligible according to the World Health Organization. The desalination performance of modified membrane showed an important salt rejection with stable water flux. In conclusion, a novel chemical method for the incorporation of Cu-mPD oligomer complex into the polyamide layer of TFC-RO membranes to improve their antibiofouling properties and desalination performance was achieved.

Influence of l-lysine on the permeation and antifouling performance of polyamide thin film composite reverse osmosis membranes.

Polyamide thin film composite (TFC) reverse osmosis (RO) membranes were prepared in this study. l-Lysine is used as a type of aqueous additive during interfacial polymerization. As a result, the pure water flux (PWF) of the resulting membranes increased by around 18% and their salt rejection improved from 98.17% to 98.40% at an optimum l-lysine dosage of 0.1 wt%. Additionally, the anti-fouling properties of the resulting membranes were enhanced. The chemical structure of the membranes was investigated using attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The morphologies of the top surface and cross-section of the membranes were revealed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM). Furthermore, contact angle (CA) and zeta potential measurements were carried out to determine the surface properties of the membranes. The results showed that the TFC RO membrane became thinner, smoother, smaller in surface area, more hydrophilic and more negatively charged after the introduction of l-lysine. Accordingly, the reason for the enhancement in the PWF and anti-fouling properties of the TFC RO membranes with the introduction of l-lysine was analyzed. The thinner selective layer (increase in concentration gradient across the membrane) with carboxyl groups (hydrogen bond interactions) and loose structure (greater free volume and sub-nanometer pores) resulted in low hydraulic resistance to the permeability of the polyamide selective layer, which led to the enhancement in PWF. Also, the smoother and more hydrophilic top surface and the increase in negative charges in the selective layer contribute to the improvement in anti-fouling property.

In-situ studies of thin-film composite reverse osmosis membranes with small-angle neutron scattering during the process of desalination

In-situ studies of thin-film composite reverse osmosis membranes with small-angle neutron scattering during the process of desalination

Influence of the sublayer structure of thin-film composite reverse osmosis membranes on the overall water flux

The support layer of RO membranes can significantly affect the permeability depending on its sublayer structure.

Recent Advances in Thin Film Composite (TFC) Reverse Osmosis and Nanofiltration Membranes for Desalination

Reverse osmosis (RO) by polymeric membranes is known to be among the successful technologies for brackish and seawater desalination. For the development of these polymeric RO membranes, two different techniques have been used – the phase inversion method for asymmetric membranes, such as cellulose acetate membrane and the interfacial polymerization for thin film composite (TFC) membranes. Despite the high quality of the water produced by TFC–RO process, TFC membranes are susceptible to fouling. After a long period of academic and industrial researches, it is generally accepted that hydrophilicity, surface charge, and surface roughness of the TFC membrane surface are the major factors which affect the membrane susceptibility to fouling. As a result, several recent studies have focused on tailoring these properties with the aim of producing TFC membranes with reduced fouling as well as enhanced flux and salt rejection for use in desalination.In this study, authors present a comprehensive summary of the most recent findings in the literature focusing on the enhancement of TFC RO and nanofiltration membrane performance in desalination applications, by tailoring membrane characteristics. The authors would then present a new concept for the preparation of TFC membranes by interfacial polymerization on porous polysulfone support using novel additives, namely, surface modifying macromolecules (SMMs). Hydrophilic SMMs (LSMMs) were synthesized both ex–situ and in–situ within the organic solvent of the TFC system. The RO performance results showed that the addition of the ex–situ LSMM significantly decreased the salt rejection of the membrane and slightly reduced the flux, while in the case of the in–situ LSMM, salt rejection was improved but the flux declined at different rates for different LSMM concentrations. The membrane prepared by the in–situ LSMM exhibited less flux decay over an extended operational period.

A novel ultra‐low energy reverse osmosis membrane modified by chitosan with glutaraldehyde crosslinking

ABSTRACTThe energy consumption of reverse osmosis (RO) has declined significantly since inception and to further decrease the energy consumption is a challenging task. The present article demonstrates the novel method to increase the membrane productivity and reduce energy consumption of desalination. Thin film composite RO (TFC RO) membrane was subjected to 2000 mg/L sodium hypochlorite for 1 h followed by varying concentrations of chitosan and glutaraldehyde for 1 h each to make a hydrophilic supra‐molecular assembly of linear polysaccharide over the polyamide layer. RO membrane exposed to 1000 mg/L chitosan and glutaraldehyde each reported 180% increase in water‐flux with about 2.7% increase in divalent ion rejection as compared to virgin TFC RO membrane. The superior performance of the membrane was explained by increased hydrophilicity as shown by decline in contact angle from 46.37° to 29.87°, increase in surface area ratio from atomic force microscope image analysis, and modification in chemical structure of polyamide from attenuated total reflectance Fourier transform infrared spectroscopy. It was further investigated that curing of glutaraldehyde treated membrane resulted in decreased water‐flux because of increase in crosslink density. Thus, an ultra‐low energy RO process can be developed based on polyamide–chitosan–glutaraldehyde membrane. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45971.

Tris(hydroxymethyl)aminomethane polyamide thin‐film‐composite antifouling reverse osmosis membrane

ABSTRACTFor the applications of reverse osmosis (RO) process, membrane fouling caused by organic molecule adsorption is still a serious problem which significantly decreases membrane lifespan and increases operation costs. In this present article, we report the thin film composite (TFC) RO membrane functionalized with tris(hydroxymethyl)aminomethane (THAM) using one‐step method for improved antifouling property. The results of surface characterization indicated that THAM was successfully grafted onto the active layer of membrane by covalent linkage. Mult‐hydroxyl‐layer was generated and remained steadily on TFC membrane surface after modification. The contact angle decreased from 75.9 ± 3.0° to 46.9 ± 2.3°, which showed a distinct improvement of membrane surface hydrophilicity after modification. The grafted THAM improved water flux by 28.3%, while salt rejection was almost unchanged in membrane property tests. The modified membranes presented preferable antifouling property to foulants of bovine serum albumin, sodium alginate, and dodecyl trimethyl ammonium bromide than that of pristine membranes during dynamic fouling experiments. The method in this study provided an effective way to improve antifouling property of the polyamide thin‐film‐composite RO membrane. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45891.

Surface modification of polyamide reverse osmosis membrane with organic-inorganic hybrid material for antifouling

Abstract A series of thin-film composite reverse osmosis membranes based on polyamide have been modified by coating the polyvinyl alcohol and 3-mercaptopropyltriethoxysilane aqueous solution prepared by a sol-gel process on the membrane surface, followed by thermal crosslinking treatment. In order to improve the hydrophilicity of the modified TFC membranes, the membranes were then immersed into H2O2 aqueous solution to convert −SH into −SO3H. The resulting TFC membranes were characterized by SEM, AFM, ATR-FTIR, streaming potential, XPS as well as static contact angle. After surface modification with the organic-inorganic hybrid material, the TFC membranes show increased NaCl rejection and decreased water flux with increasing 3-mercaptopropyltrimethoxysilane content in coating solution. The optimal modification membrane (PA-SMPTES-0.8) exhibits a NaCl rejection of 99.29%, higher than that (97.20%) of the virgin PA membrane, and a comparable water flux to virgin PA membrane (41.7 L/m2 h vs 47.9 L/m2 h). More importantly, PA-SMPTES-0.8 membrane shows much more improved fouling resistance to BSA than virgin PA and PVA modified PA (PA-PVA-1.0) membranes. PA-SMPTES-0.8 membrane loses about 13% of the initial flux after BSA fouling for 12 h, which is lower than that of virgin PA and PA-PVA-1.0 membranes (42% and 18%). Furthermore, the flux recovery of PA-SMPTES-0.8 membrane reaches 94% after cleaning. Thus the TFC membranes modified by this organic-inorganic hybrid technology show potential applications as antifouling RO membrane for desalination and purification.

Performance Enhancement of PA-TFC RO Membrane by Using Magnesium Silicate Nanoparticles

This study focuses on to the change of the execution of polyamide (PA) thin-film composite (TFC) reverse osmosis (RO) membrane utilizing surface alteration by MgSiO3 nanoparticles. This has been an expert by means of holding of the practical grafting of PA layer with magnesium silicate nanoparticles (MgSiO3) in the presence of 2-acylamido 2-methyl propane sulphonic acid (AMPS) as condensing monomer. To confirm the presence of MgSiO3 nanoparticles and to inspect the morphology of the TFC nanoparticles layer SEM, FT-IR, XRD, TGA and DMA analysis were used. The outcomes demonstrated that the AMPS are effectively joined on the TFC film surface with an upgrade in thermal and mechanical decencies contrasted with pristine TFC layer. Besides, the contact angle estimations demonstrate an increase in the hydrophilicity of the thin film surface by the addition of nanoparticles. The water flux and salt rejection of the modified membranes were 25 L/m2 h and 95.5%, respectively.

Activation promoted ionic liquid modification of reverse osmosis membrane towards enhanced permeability for desalination

Abstract The ionic liquid (1,3-dimethylimidazolium dimethyl phosphate ([MMIM][DMP])) synthesized by addition reaction was used to modify a commercial reverse osmosis (RO) membrane thorough activation method. The activation promoted modification process was completed within just 6−12 min under optimal condition of the immersion time of 4 min, activation temperature of 110 °C and activation time of 4 min. The variation of surface morphologies and properties of the RO membrane were characterized by SEM, AFM, water contact angle, FTIR, and the RO performance was evaluated by desalination of 1000 mg⋅L−1 NaCl aqueous solution. The results showed that the active layer of the modified RO membrane became thinner, smoother, and more hydrophilic with increasing of activation temperature. The IL modified membrane achieved water flux of 33.7 L m−2 h−1 and rejection of 93.2%, showing 62% higher water flux comparing to the pristine membrane and 2.6% decrease in salt rejection. Moreover, the IL modified membrane showed an enhanced anti-fouling property with 95.5% of normalized water flux recovery. This work provides a facile and efficient way to modify and improve separation performance and anti-fouling property of commercial thin film composite (TFC) RO membranes.

Incorporation of CuO nanoparticles into thin-film composite reverse osmosis membranes (TFC-RO) for antibiofouling properties

The effect of the incorporation during the interfacial polymerization process of copper-oxide (CuO) nanoparticles in thin-film composite (TFC) reverse osmosis (RO) membrane on their antibiofouling and desalinization performance have been studied. Membranes were characterized by fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM), zeta potential and contact angle measurements. Bactericidal tests were performed using Escherichia coli and anti-adhesion properties were confirmed by fluorescence microscopy. Membrane performance using a cross flow cell was evaluated. XRD and SEM–EDX analyses confirmed the incorporation of these nanoparticles into the membrane. Similar contact angle, higher surface roughness and less negatively charged surface on modified membrane compared to that of the pristine membrane were observed. However, an excellent anti-adhesion and bactericidal effect were observed, mainly attributed to the copper toxicity. The desalination performance of the modified membrane showed an important salt rejection with stable water flux. In conclusion, the incorporation of CuO nanoparticles into TFC-RO membranes during the interfacial polymerization process is a potential alternative method to improve the antibiofouling capacities without impairing the performance of the membrane.

Preparation and characterization of a thin-film composite reverse osmosis membrane using a polysulfone membrane including metal-organic frameworks

The objectives of this paper were to elucidate the performance of a thin-film composite (TFC) reverse osmosis (RO) membrane by modifying the support layer. In order to improve the hydrophilicity and porosity of the support layer, we prepared a polysulfone (PSf) membrane containing an HKUST-1 [Cu3(BCT2)] metal organic framework (MOF) treated with sulfuric acid for the stability of water. N,N-dimethylformamide (DMF)/water was used as the solvent/non-solvent pair, and the TFC RO membrane was formed by the interfacial polymerization of m-phenylene diamine (MPD) in aqueous solution with trimesoyl chloride (TMC) in organic solution on the MOF/PSF support layer. The optimized concentration of MPD-TMC was investigated through XPS, and the manufactured membrane had a thin, smooth film when paired with a hydrophilic and porous support layer. The active layer thickness of novel membrane was 0.029µm via FTIR analysis that the thickness compared to a commercial RO membrane having a thickness of 0.2µm. Also, the novel membrane showed improved flux and fouling resistance compared to the TFC RO membrane with a PSF support layer, without altering the salt rejection property.

Thin-film nanofibrous composite reverse osmosis membranes for desalination

Interfacial polymerization of m-phenylenediamine (MPD) and trimesoyl chloride (TMC) was carried out on top of the highly permeable nanofibrous ultrafiltration (UF) membrane substrates to create thin-film nanofibrous composite (TFNC) reverse osmosis (RO) membranes for desalination. The UF substrates contained distinct fibrous layers: poly(ethylene terephthalate) (PET) non-woven mat as the mechanical support, electrospun polyacrylonitrile (PAN) nanofibrous scaffold as the mid-layer or barrier layer, and ultra-fine cellulose nanofibers (CNs) as the barrier layer. An aliphatic co-monomer, piperazine (PIP) and different additives (e.g. an ionic liquid 1-octyl-3-methylimidazolium chloride, OMIC) were included in interfacial polymerization to improve the permeation flux for RO operations. To further increase the membrane permeability, a spray coating method was also used to control the barrier layer thickness by adjusting the load of the aqueous solution in polymerization. The optimized RO membrane exhibited a rejection ratio of 96.5% against NaCl (500ppm) and a flux of 28.6L/m2h at 0.7MPa, approaching the performance of a high-flux commercial RO membrane (DOW FILMTEC™ XLE). We believe higher permeation flux can be achieved using nanocomposite barrier layer with the CN-based UF substrate, while still maintaining high salt rejection ratio.